1. Field of the Invention
The present invention relates in general to a marine propulsion system, and more particularly to a shifting system for an outboard drive.
2. Description of Related Art
Many forms of outboard drives employ forward, neutral, reverse transmissions together with a double propeller construction. Such transmissions are common in both outboard motors and in the outboard drive units of inboard-outboard motors.
These transmissions typically include a driving bevel gear and a pair of oppositely rotating driven bevel gears that are journaled within a lower unit of the outboard drive. A front dog clutch of a dual clutch assembly selectively couples an inner propeller shaft to one of the driven bevel gears to rotate a first propeller shaft in a forward or a reverse direction. A rear dog clutch of the clutch assembly selectively couples an outer propeller shaft to the rear driven bevel gear to rotate a second propeller in the forward direction.
A common actuator conventionally engages the clutches with their respective gears. That is, one actuator simultaneously engages the front dog clutch and the front gear, and the rear dog clutch and the rear gear.
A conventional actuator involves a plunger actuated by a cam. A spring, acting on an opposite end of the plunger from the cam, forces the plunger to follow the cam. To engage the front clutch with the front gear and to engage the rear clutch with the rear gear, the spring forces the clutches to engage the gears. To engage the front clutch with the rear gear, the cam forces the front clutch to engage the rear gear.
Several drawbacks are associated with conventional transmissions of the type described above. Simultaneous engagement of the clutches requires synchronized registration of both the teeth of the front clutch and front gear, and the teeth of the rear clutch and rear gear. The teeth of the gears and clutches are not static, however, and synchronization of the teeth is not a constant condition. Under most conditions, the teeth of the clutches and gears are out of phase. Thus, engagement may not be instantaneous, and may not be as quick as the watercraft operator would like.
Additionally, the simultaneous engagement of the front and rear clutches with their respective gears produces a large mechanical shock on the transmission. This mechanical shock accelerates fatigue and wear in the transmission components, as well as in the other component of outboard drive.